Heat-resistant abrasive wheels



HEAT-RESISTANT WHEELS Louis E. Vigliatura, Jr., Worcester, Mass.

No Drawing. Filed Jan. 2, 1958, Ser. No. 706,542 4 Claims. (Cl. 51-298) This invention relates to resinoid bonded abrasive wheels and is particularly concerned with heat-resistant abrasive wheels having resinoid bonds.

In the copending application of H. Nathan Stone, Serial No. 706,541, filed contemporaneously herewith, there is described and claimed the use of cryolite and ammonium chloride as fillers in sulfur-free, resinoidbonded abrasive wheels intended for grinding stainless steel. Such grinding wheels in performance are equal to or better than the wheels which were previously standard and which employed metallic sulfides as fillers and are also advantageous since the swarf resulting from their use contains no sulfur. However, in very severe use they occasionally have some tendency to spall and develop radial cracks as a result of unequal thermal expansion.

It is an object of the present invention to provide sulfur-free, resinoid-bonded abrasive wheels suitable for grinding stainless steel that are resistantto thermal spalling and cracking. 7

Another object of the invention is to provide abrasive wheels of the character described which have relatively high cutting rates and efiiciencies in grinding stainless steels.

Other objects and advantages of the present invention will be evident from the following description thereof;

The objects set out above are achieved in the practice of the invention by using suitable proportions of chilled iron grit with the cryolite and ammonium; chloride fillers described in above-mentioned cdpending application. In the following example there is described the manufacture of a 20" x 2 /2" x 6 snagging wheel in accordance 'with the present invention. It will be understood that the procedure set forth is only exemplary and that otherprocedures may be used.

Example I The following materials are used:

Wt. in lbs. Fused alumina abrasive (14 grit) 62.70

Powdered phenol-formaldehyde resin, (such. as

Bakelite BR-2417) 9250 Powdered cryolite (approximately 200 mesh) 9';21 Granular ammonium chloride (30 mesh and finer) t 7 2:06 Chilled iron grit (approximately 200me'sh) li63 Powdered lime (CaO) (approximately 200 mesh) Furfural, 140-285 cc.

States Pate 0 pressed wheel is then removed from the mold and further cured by heating in an oven held at 350 F. for 24 hours. The cured wheel, which comprises about 54% abrasive grain and 46% bond, by volume, may be finished according to the well known and conventional procedures used in the art.

As indicated above, other procedures for making abrasive wheels according to the invention may be employed; Thus, conventional cold pressing methods may be used or the hot pressing procedure described may be modified according to known practices. Also it will be understood that other types of heat-setting and resistant resinoid bonds, such as aniline-formaldehyde and resorcinolformaldehyde resins and the like may be' substituted for the phenol-formaldehyde resin of the example. Further, as will be seen from the further description of the invention, the proportions of ingredients used may be varied considerably.

In Example I, the cryolite, ammdnium chloride and chilled iron grit constituted by volume, respectively, about 23%, 10% and 10% of the total bond. It has been found that good results are obtainable when the bond comprises, by volume, from about 40%45% of the mixture of fillers. Examples of suitable mixes are illustrated below.

In the following examples the comparative grinding tests were carried out on No. 410 stainless steel using 20" x 2 /2" x 6" abrasive wheels with fused alumina abrasive running at 8500 s.f.p.m. In each example the wheel identified as A contained cryolite, amnionium chloride, and chilled iron grit as fillers in a resinoid bond, but wassulfur-free. The wheel identified as S in each example was typical of commercially available wheels previously used in snagging stainless steel billets, the resinoid bond including zinc sulfide as a filler. The wheels compared in each instance, however, had approximately the'same volume ratios of abrasive grain to bond.

Example 11 M W Wheel- Metal Wheel Efficiency Removed; Loss, M/W

lbs/hr. ins/hr.

A 28. 4 28. 3 l. 0 S--- 28.4 29.6 0.96

It is evident that wheel A was substantially equivalent to wheel S since the metal removal rate was the same andthe efiiciencies' were not significantly difierent.

Example III An abrasive wheel the resinoid bond of which con tained, by volume, 5% chilled iron grit, 27% cryolite and 10% ammonium chloride as fillers was tested in comparison with an abrasive wheel of similar structure that included 16% by volume of zinc sulfide as a filler in the bond. The results (averages) were:

M W Wheel Metal Wheel Efiiciency Removed, Loss, M/W

lbs/hr. lnfi/hr.

While the efl'iciency of wheel S was very slightly greater, the cutting rate of wheel A was significantly better.

Example IV An abrasive wheel containing as fillers in the bond thereof 2% chilled iron grit, 10% ammonium chloride and 30% cryolite, all by volume, was tested against a wheel of similar structure including 16% of zinc sulfide (by volume) in the bond. The following table shows the results as averages:

A resinoid bonded, sulfur-free grinding wheel having as fillers in the bond chilled iron grit, cryolite, and ammonium chloride in, respectively, 12%, 20% and 10% by volume was compared in tests with a grinding wheel of similar size and structure formed with a bond which included 16% by volume of zinc sulfide filler. The test results (averages) were:

M W Wheel Metal Wheel Eflileiency Removed, Loss, M/W

lbs/hr. in 3 In Examples IV and V the wheels identified as A in each case difiered only slightly in both metal removal and efficiency from those identified as S."

It will be evident from the test results of Examples 11 to V that grinding wheels according to the present invention are in performance quite satisfactory as substitutes for the metallic sulfide containing wheels previously employed in grinding stainless steel billets. This has been further demonstrated by actual field tests. In field tests it has also been found that there is no tendency for wheels according to the present invention to spall or develop radial cracks as a result of unequal thermal expansion. It has additionally been determined that bonds of the types with which the present invention is concerned have an average tensile strength about 22% greater than the bonds of commercially available grinding wheels including zinc sulfide as a. filler.

As pointed out above the total filler content of the wheel bond is preferably from about 40% to 45% by volume. Within this range total the cryolite may vary from about 20% to 38%, the ammonium chloride may be from about to 15% and the chilled iron grit may vary from about 2% to 15%.

The chilled iron grit employed as a novel filler in abrasive wheels according to the present invention is a commercial product obtained by fine crushing of chilled iron or so-called white cast iron in which the carbon is mainly retained in combined form as cementite. While 200 mesh chilled iron grit is quite satisfactory, the mesh size may vary between about to 325 if desired. The cryolite filler may vary in mesh size similarly although there too a particle size that will pass through a 200 mesh screen is preferred. Because of its hydroscopicity, the ammonium chloride is preferably no finer than 100 mesh and satisfactory results are obtained with 30 mesh ammonium chloride. The lime listed as an ingredient of the mix in the typical wheel making procedure of Example I is present as a conventional ingredient to absorb water produced during cure of the resin of the bond. The amount used is not critical but enough should be employed to accomplish the desired purpose which is to prevent the wheel bloating during the cure. The necessary amounts for dilferent types of resins are known to tho'se skilled in the art.

It will be understood that the present invention is subject to variation from and modification of the specific details set forth above. Thus, for example, the abrasive grain used may vary in grit size and if desired a mixture of several grit sizes may be employed. Also, the proportions of abrasive and bdnd may be altered to obtain desired results. It is, therefore, intended that the invention should not be construed narrowly, but should be given as broad an interpretation as is permitted by the appended claims.

I claim:

1. A sulfur-free abrasive wheel which consists of abrasive granules and a bond, said bond comprising essentially a heat-hardenable resin, about 23% by volume of cryolite, about 10% by volume of ammonium chloride, and about 10% by volume of chilled iron grit.

2. A sulfur-free abrasive wheel which consists of abra sive granules and a bond, said bond comprising essentially a heat-hardenable resin, and as a filler mixture about 20% to 38% by volume of cryolite, about 5% to 15% by volume of ammonium chloride, and about 2% to 15% by volume of chilled iron grit, the total volume of said filler mixture being from about 40% to 45%.

3. A sulfur-free abrasive wheel as set forth in claim 2 in which the mesh sizes of the fillers fall within the following approximate limits-crydlite: 100 mesh-325 mesh, ammonium chloride: 30 mesh-100 mesh, chilled iron grit: 100 mesh-324 mesh.

4. A sulfur-free abrasive wheel as set forth in claim 1 in which the mesh sizes of the fillers fall within the following approximate limits-cryolite: 100 mesh-325 mesh, ammonium chloride: 30 mesh-100 mesh, chilled iron grit: 100 mesh-325 mesh.

References Cited in the file of this patent UNITED STATES PATENTS 2,162,600 Ball June 13, 1939 2,333,429 Kuzmick Nov. 2, 1943 2,534,806 Webber et a1. Dec. 19, 1950 2,811,430 Gregor et al Oct. 29, 1957 2,860,960 Gregor Nov. 18, 1958 2,860,961 Gregor et al. Nov. 18, 1958 

2. A SOLFUR-FREE ABRASIVE WHEEL WHICH CONSISTS OF AORASIVE GRANULES AND A BOND, SAID BOND COMPRISING ESSENTIALLY A HEAT-HARDENABLE RESIN , AND A FILLER MIXTURE ABOUT 20% TO 38% BY VOLUME OF CRYOLITE, ABOUT 5% TO 15% BY VOLUME OF AMMONIUM CHLORIDE, AND ABOUT 2% TO 15% BY VOLUME OF CHILLED IRON GRIT, THE TOTAL VOLUME OF SAID FILLER MIXTURE BEING ABOUT 40% TO 45%. 